It is known that color photographic images are produced upon development of the light-sensitive silver halides of the photographic elements. A silver image is produced upon reduction of the silver ions with primary aromatic amine type developer compounds in the presence of color couplers which react with the oxidized developer to form a dye in the regions corresponding to the silver image. The substractive three-color photographic process makes use of light-sensitive color photographic elements which include, coated on a support base, one or more red-sensitized silver halide emulsion layers, one or more green-sensitized silver halide emulsion layers and one or more blue-sensitized silver halide emulsion layers, wherein cyan, magenta and yellow dye images are respectively formed upon color development of proper couplers.
The couplers normally used to produce cyan image dyes derive from phenols and naphthols (as for instance described in U.S. Pat. Nos. 2,367,351; 2,423,730; 2,474,293; 2,772,161; 2,772,162; 2,895,826; 2,920,961; 3,002,836; 3,476,563; 3,880,661; in FR Pat. Nos. 1,478,188 and 1,497,403 and in GB Pat. No. 2,070,000). Such couplers can be used either in the baths or in the photographic layers. In the latter case, they can bear ballasting substituents if they are desired not to migrate into the layers and, respectively, hydrophilic or hydrophobic substituents if they are to be introduced into the photographic layer dissolved either in water or in an organic solvent. Upon reaction with the oxidation products of the aromatic primary amino type developing agents, such couplers give indoaniline dyes with consumption of four equivalents of silver ions per mole of dye and preferably two equivalents of silver ions per mole of dye when the reactive methine group (in para position to the phenolic hydroxyl) is substituted by atoms and groups which are splitted off during the coupling reaction (in this latter case the couplers are called 2-equivalent couplers). In the practical use of the cyan-dye forming couplers in the photographic processings, some characteristics of the dyes formed by said couplers after development are thought to be very important in the choise of the couplers, i.e. stability to light, heat and humidity, stability towards the reduction of ferrous ions present in the processings. The loss of density due to an insufficient stability of the dye is the cause of color unbalance in the developed photographic material. Such loss occurs with indoaniline dyes when the bleach and bleach-fixing baths have an insufficiently high redox potential (when, for instance, in the bleach bath containing ferric ions there is a too high concentration of ferrous ions).
To find new classes of dye-forming couplers with characteristics suitable for an optimal use in the photographic materials is desirable even if difficult to be performed.